extend distribution_version tests

Author: RonnyPfannschmidt

test_apipkg.py

@@ -531,6 +531,7 @@ def test_initpkg_without_old_module():
 def test_get_distribution_version():
     assert apipkg.distribution_version('setuptools') is not None
     assert apipkg.distribution_version('email') is None
+    assert apipkg.distribution_version('py') is not None
 
 
 def test_eagerload_on_bython(monkeypatch):